1. Field of the Invention
The present invention relates to outsoles for athletic shoes, particularly those for shoes, such as running shoes, in which the sole has a shock absorbing midsole layer on the outside of which a wear resistant outsole with a tread surface is applied. More specifically, the present invention to an outsole of this type which has tread elements affixed to a thin flexible sheet material that is cemented to the underside of the at least portions of the midsole. The invention also relates to a method of making such an outsole.
2. Description of Related Art
For some time now virtually all athletic shoes have been made with soles that are comprised of a shock absorbing midsole layer on the outside of which a wear resistant outsole with a tread surface is applied. The midsole is typically formed of a lightweight, soft foam material, such as a polyurethane foam, with or without weight-reducing and/or shock absorbence or distribution inserts, such as air bladders, honeycombs, gels, etc. On the other hand, the outsole has been formed of a hard, molded material, such as a thermoplastic elastomer such as PVC, synthetic rubber, etc. Because such outsole materials are relatively stiff and heavy, efforts have been made to reduce the area of the sole that is covered by the outsole, leaving gaps, e.g., in the arch area and portions of the heel which usually do not contact the ground. Likewise, the outsole has been provided with zones of increased flexibility, e.g., areas of thin wavy areas in the zone of the ball of the foot and other joint areas. However, all of these measures complicate the manufacturing process without optimizing the reduction of weight attributable to the outsole or minimizing the stiffening effect of the outsole.
In a departure from usual outsole construction practice, the DuoSole.RTM. outsole of the Asics Corporation uses a sheet of a synthetic suede fabric as a base layer to one side of which a uniform pattern of thermoplastic polyurethane tread elements is attached, apparently by cementing. Suitably shaped segments of the fabric are cut from the sheet (tread portions at the periphery of the segments also being cut) and then opposite side of the sheet from that having the tread elements is cemented directly onto desired portions of the midsole.
In this manner, outsoles which are significantly lighter and more flexible than those produced using conventional techniques can be obtained. On the other hand, while the specific technique by which the tread elements are attached to the fabric base layer is unknown, it is readily apparent from an examination of shoes with these soles that have been manufactured for the past three years, that the process makes it impractical to form or apply other than a uniformly distributed repeating pattern (analogous to repeating patterns on wallpaper) of relatively small tread elements that are all the same. This factor makes this technique unsuitable for requiring larger treads than are suitable for running shoes (e.g, cross trainers and shoes hiking shoes) and prevents optimizing of the tread pattern with different treads in different areas or applying of localized decorative, trademark or other designs to the tread surface. Still further, this manner of formation results in a substantial wasting of tread material since a significant number of tread elements will be located on areas of the based layer outside of the area(s) cut out. It has also been noted that in some instances a laminate base material construction has been used; but, such uses can result in the inner layer which is affixed to the sole separating from the outer layer to which the tread elements are affixed, which is clearly undesireable.
In an unrelated field, a geotextile having a uniformly distributed pattern nodules of a time-release soil treatment compound bonded to a flexible porous sheet material, such as a woven or nonwoven web of polypropylene filaments is known (U.S. Pat. No. 5,139,566). In particular, in one method of forming this geotextile, a mixture of an active agent and a binder is injected or forced under pressure through the porous web into an array of shaping cavities, over the open ends of which the web is held. The mixture is then allowed to solidify so that the web becomes entrapped within the nodules formed, the web having deformed/bulged into the open ends of the cavities. This process is dependent upon the porosity of the sheet material and the fluidity of the mixture being forced through it.
Thus, this process is not directly applicable to shoe outsole manufacturing where it is not desirable for the base material to be porous and where the tread material is highly viscous, even when molten. Furthermore, the disclosure is not oriented toward the various other considerations relevant to shoe sole manufacturing that are of no consequence in producing a soil treatment product.